Lactic acid-producing microorganisms (e.g., Lactobacillus) play an important role in the maintenance of healthy vaginal ecology. Some even believe that healthy vaginal ecology is primarily dependant upon specific, native lactic acid-producing microorganisms (e.g., lactobacilli). Some common lactobacilli strains found in the vagina include Lactobacillus jensenii; Lactobacillus gasseri; Lactobacillus salivarius; and Lactobacillus casel. 
The specific composition of the microbiota has a major impact on vaginal health, as colonization of several undesirable organisms may result in bacterial vaginosis, candidiasis, or other diseases. Undesirable organisms include Gardnerella, Candida, and other opportunistic pathogens. Interestingly, colonization of these opportunistic pathogens appears to be far less common when the vaginal microbiota is well populated by lactobacilli.
Bacterial vaginosis is a microecologic condition in which there are dramatic alterations in the endogenous vaginal microflora. Specifically, bacterial vaginosis involves a reduction in the overall number of lactic acid-producing bacterial strains, with a concomitant multi-log population increase in a characteristic set of microflora including, but not limited to Gardnerella vaginalis, genital anaerobes, and mycoplasmas.
Bacterial vaginosis if left untreated can lead to potentially serious heath concerns for the woman and even an unborn child. Both observational and interventional studies have shown that bacterial vaginosis in the early stages of pregnancy is associated with pre-term delivery and, in later stages of gestation, miscarriage. These studies suggest that bacterial vaginosis may be a direct cause of adverse outcomes in pregnancy, rather than simply being a surrogate marker. Studies also suggest that ascending infection or abnormal lower reproductive tract microflora mediate adverse pregnancy outcomes.
Bacterial vaginosis can be mitigated by lactic acid producing (i.e., probiotic) organisms. As previously discussed, the cause-and-effect relationship in bacterial vaginosis is due to the reduction of lactic acid-producing bacterial strains with the resulting multi-log increases of anaerobic microorganisms including, but not limited to, Gardnerella vaginalis. However, the results of a recent 3900-woman study performed in Denmark demonstrated that absence of bacterial vaginosis was directly associated with sufficient vaginal colonization of aerobic lactic acid-producing organisms.
There have been attempts to develop products and/or methodologies that utilize hydrogen peroxide producing Lactobacilli as a vaginal suppository therapy for the amelioration of vaginal yeast infections, but viability of these microorganisms continues to be the main difficulty in the use of Lactobacilli in those formulations.